Nowadays, large-capacity magnetoresistive random access memories (MRAMs) using a magnetic tunnel junction (MTJ) element exploiting the tunnel magnetoresistive (TMR) effect have gained attention and raised expectations. In an MTJ element used for an MRAM, one of two ferromagnetic layers (CoFeB) holding a tunnel barrier layer (MgO) therebetween is used as a magnetization fixed layer (reference layer) in which the direction of magnetization is fixed and prevented from changing, and the other is used as a magnetization free layer (storage layer) in which the direction of magnetization is easily reversed. The state where the directions of magnetization of the reference layer and the storage layer are parallel and the state where the directions of magnetization are antiparallel are correlated with binary numbers “0” and “1”, respectively, and thereby information can be stored.
When the directions of magnetization of the reference layer and the storage layer are parallel with each other, the resistance (barrier resistance) of the tunnel barrier layer is lower than that in the case where the directions of magnetization are antiparallel, and has greater tunnel current. The equation “MR ratio=(resistance in the antiparallel state−resistance in the parallel state)/resistance in the parallel state” holds. Stored information is read out by detecting a change in resistance caused by the TMR effect. Thus, it is preferable that a resistance change rate (MR ratio) caused by the TMR effect is large in reading.